1. Field of the Invention
The present invention relates to a liquid pump and an inkjet printer provided with the pump.
2. Description of the Related Art
In the inkjet recording device, it is common to use a liquid pump in supplying, circulating and wasting ink. The liquid pump comes in various types.
Recently, there are increasing tendencies to use a larger number of types of ink for one inkjet recording device to record high quality images.
Therefore, when ink to be used is supplied by a liquid pump, it not only indicates a large device, but also produces a costly device to provide the same number of liquid pump power sources as the number of liquid pumps, that is, the same number of types of ink.
The Japanese Published Patent Application No. 2002-307724 discloses a pump (liquid pump) capable of relatively easily incorporating power sources into one unit.
FIG. 1 shows the outline of an ink system for a printer in the Japanese Published Patent Application No. 2002-307724, and FIG. 2 shows the configuration of the pump according to the same Japanese Published Patent Application No. 2002-307724. As shown in FIG. 1, the ink system is configured by an ink head 301, an ink head recovery unit 78, a subtank 307, an ink pump 331, an ink bag 310a, a waste ink absorber 310b, and one-way valves 326 and 327 capable of passing ink only when the condition of the pressure is satisfied such that the ink can pass in the direction indicated by the arrow mark shown in FIG. 1.
The ink pump 331 is configured by a motor P13 as a driving source, an ink supply pump unit P16, and a waste ink collection pump unit P18 as shown in FIG. 2.
The ink supply pump unit P16 and the waste ink collection pump unit P18 are provided with a roller P17 for depressing a tube P20. The ink supply pump unit P16 is fixed to a pump shaft P15 directly coupled to the motor P13 such that the pump can rotate in both normal and reverse directions. The waste ink collection pump unit P18 includes a one-way clutch P21, and can rotate only when the motor P13 rotates in the reverse direction.
The pump according to the Japanese Published Patent Application No. 2002-307724 can also be configured by a gear pump etc. in addition to the above-mentioned tube pump.
Thus, when the motor P13 normally rotates, the ink is supplied from the ink bag 310a to the subtank 307 through the one-way valve 327. When the motor P13 inversely rotates, the ink is supplied from the subtank 307 to the head 301 through the one-way valve 326, and simultaneously the waste ink in the ink head recovery unit 78 is collected by the waste ink absorber 310b. 
FIG. 1 is an explanatory view of the ink system about one color of a printer. When the number of colors to be used increases, the number of coupled pump units corresponding to the number of used colors as shown in FIG. 3, thereby successfully using a number of colors with one driving source.
The pump according to the Japanese Published Patent Application No. 2002-307724, one driving source can be used for an increasing number of colors to be used as if the number of pump units logically increased.
However, the pump unit according to the Japanese Published Patent Application No. 2002-307724 is configured by a tube pump and a gear pump, and has the following disadvantages in durability and reliability requested for a recent inkjet recording device.
That is, a tube pump conveys ink by pressing the outside of the tube P20 containing the ink by the roller P17.
Therefore, there is the possibility that the tube P20 is broken, and the tube P20 requires specifically high flexibility and chemical resistance, thereby resulting in a costly pump.
In addition, a gear pump can generate ground powder from a rotating and rubbing gear portion. If the ground powder etc. is mixed with ink, it may cause defective ink jet of the ink head.